[Qemu-devel] [PATCH v2 04/14] qapi: Factor out JSON number formatting

[Eric Blake <eblake@redhat.com>]

Pull out a new qstring_append_json_number() helper, so that all
JSON output producers can use a consistent style for printing
floating point without duplicating code (since we are doing more
data massaging than a simple printf format can handle).

Address one FIXME by adding an Error parameter and warning the
caller if the requested number cannot be represented in JSON;
but add another FIXME in its place because we have no way to
report the problem higher up the stack.

Signed-off-by: Eric Blake <eblake@redhat.com>

---
v2: minor wording tweaks
---
 include/qapi/qmp/qstring.h |  4 +++-
 qobject/qobject-json.c     | 24 +++---------------------
 qobject/qstring.c          | 37 ++++++++++++++++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 23 deletions(-)

diff --git a/include/qapi/qmp/qstring.h b/include/qapi/qmp/qstring.h
index 1a938f6..cab1faf 100644
--- a/include/qapi/qmp/qstring.h
+++ b/include/qapi/qmp/qstring.h
@@ -1,7 +1,7 @@
 /*
  * QString Module
  *
- * Copyright (C) 2009 Red Hat Inc.
+ * Copyright (C) 2009, 2015 Red Hat Inc.
  *
  * Authors:
  *  Luiz Capitulino <lcapitulino@redhat.com>
@@ -15,6 +15,7 @@

 #include <stdint.h>
 #include "qapi/qmp/qobject.h"
+#include "qapi/error.h"

 typedef struct QString {
     QObject base;
@@ -32,6 +33,7 @@ void qstring_append_int(QString *qstring, int64_t value);
 void qstring_append(QString *qstring, const char *str);
 void qstring_append_chr(QString *qstring, int c);
 void qstring_append_json_string(QString *qstring, const char *raw);
+void qstring_append_json_number(QString *qstring, double number, Error **errp);
 QString *qobject_to_qstring(const QObject *obj);
 void qstring_destroy_obj(QObject *obj);

diff --git a/qobject/qobject-json.c b/qobject/qobject-json.c
index 1557ec6..dbe0ab8 100644
--- a/qobject/qobject-json.c
+++ b/qobject/qobject-json.c
@@ -176,27 +176,9 @@ static void to_json(const QObject *obj, QString *str, int pretty, int indent)
     }
     case QTYPE_QFLOAT: {
         QFloat *val = qobject_to_qfloat(obj);
-        char buffer[1024];
-        int len;
-
-        /* FIXME: snprintf() is locale dependent; but JSON requires
-         * numbers to be formatted as if in the C locale. */
-        /* FIXME: This risks printing Inf or NaN, which are not valid
-         * JSON values. */
-        /* FIXME: the default precision of %f may be insufficient to
-         * tell this number apart from others. */
-        len = snprintf(buffer, sizeof(buffer), "%f", qfloat_get_double(val));
-        while (len > 0 && buffer[len - 1] == '0') {
-            len--;
-        }
-
-        if (len && buffer[len - 1] == '.') {
-            buffer[len - 1] = 0;
-        } else {
-            buffer[len] = 0;
-        }
-
-        qstring_append(str, buffer);
+        /* FIXME: no way to report invalid JSON to caller, so for now
+         * we just ignore it */
+        qstring_append_json_number(str, qfloat_get_double(val), NULL);
         break;
     }
     case QTYPE_QBOOL: {
diff --git a/qobject/qstring.c b/qobject/qstring.c
index 2882c47..b06f290 100644
--- a/qobject/qstring.c
+++ b/qobject/qstring.c
@@ -1,7 +1,7 @@
 /*
  * QString Module
  *
- * Copyright (C) 2009 Red Hat Inc.
+ * Copyright (C) 2009, 2015 Red Hat Inc.
  *
  * Authors:
  *  Luiz Capitulino <lcapitulino@redhat.com>
@@ -13,6 +13,7 @@
 #include "qapi/qmp/qobject.h"
 #include "qapi/qmp/qstring.h"
 #include "qemu-common.h"
+#include <math.h>

 /**
  * qstring_new(): Create a new empty QString
@@ -165,6 +166,40 @@ void qstring_append_json_string(QString *qstring, const char *raw)
 }

 /**
+ * qstring_append_json_number(): Append a JSON number to a QString.
+ * Set @errp if the number is not representable in JSON, but append the
+ * output anyway (callers can then choose to ignore the warning).
+ */
+void qstring_append_json_number(QString *qstring, double number, Error **errp)
+{
+    char buffer[1024];
+    int len;
+
+    /* JSON does not allow Inf or NaN; append it but set errp */
+    if (!isfinite(number)) {
+        error_setg(errp, "Non-finite number %f is not valid JSON", number);
+    }
+
+    /* FIXME: snprintf() is locale dependent; but JSON requires
+     * numbers to be formatted as if in the C locale. */
+    /* FIXME: the default precision of %f may be insufficient to
+     * tell this number apart from others. */
+    len = snprintf(buffer, sizeof(buffer), "%f", number);
+    assert(len > 0 && len < sizeof(buffer));
+    while (len > 0 && buffer[len - 1] == '0') {
+        len--;
+    }
+
+    if (len && buffer[len - 1] == '.') {
+        buffer[len - 1] = 0;
+    } else {
+        buffer[len] = 0;
+    }
+
+    qstring_append(qstring, buffer);
+}
+
+/**
  * qobject_to_qstring(): Convert a QObject to a QString
  */
 QString *qobject_to_qstring(const QObject *obj)
-- 
2.4.3